This article explores results from a research project studying teacher learning and faculty teaching in two online courses for teachers in a master's degree program. We focus on the interactions among students in online small-group discussions. We argue that three aspects of the online courses impact the way students enter into discussions online, and consequently, what they have opportunities to learn: (a) the subject matter itself, (b) the representations and media through which the subject matter is engaged, and (c) the tasks students are asked to carry out online. In addition, we argue that students' disposition to engage in constructive discourse (or not) is an important and only partly controllable factor in what happens in online discussion. (Contains 1 note.)